This invention relates to a silver/silver halide electrode and further relates to an ion-selective silver/silver halide electrode element which is favorably employable for analysis of concentration of a biochemically active ion existing in body fluids such as blood, urine, and saliva.
Various ions existing in body fluids, such as sodium ion, potassium ion, chloride ion, bromide ion, and iodide ion, can be quantitatively detected by means of an ion-selective silver/silver halide electrode element. Representative structure of the ion-selective silver/silver halide electrode element comprises, in order, a non-electroconductive support sheet, an electrode composite consisting essentially of a silver metal layer and a silver halide layer, an electrolytic material layer, and an ion-selective layer, the electrode composite being divided to give a pair of electrode units, and further comprising a referential liquid-receiving area and a sample liquid-receiving area each of which is provided on the ion-selective layer above each electrode unit, and an electroconductive bridge having two terminals, one terminal being placed in the referential liquid-receiving area and another terminal being placed in the sample liquid-receiving area.
The silver halide layer on the silver metal layer is generally produced by oxidizing the silver metal layer on its surface with an oxidizing compound in the presence of a halide containing a halide ion such as chloride ion.
Japanese Patent Provisional Publications No. 56-33537 and 56-33538 (corresponding to U.S. Ser. No. 66123 and No. 66124, respectively) describe the silver metal layer is oxidized using KClCrO3, K3Fe(CN)4, KMnO4, K2Cr2O7, NH4VO3, (NH4)2Ce(NO3)6, or Fe2(C2O4)3, to prepare a silver/silver halide electrode.
As a result of studies performed by the present inventors, it has been discovered that an ion-selective silver/silver halide electrode element containing a silver halide layer which is produced by oxidizing the silver metal layer with a heavy metal element-containing oxidizing compound such as KMnO4 or K2Cr2O7, sometimes does not give a reliable analytical result.
Accordingly, it is an object of the present invention to provide an ion-selective silver/silver halide electrode element and a silver/silver halide electrode favorably employable for its manufacture.
The present invention resides in a silver/silver halide electrode comprising a non-electroconductive support sheet, a silver metal layer, and a silver halide layer, in order, wherein the silver halide layer contains essentially no heavy metal element.
The silver halide layer of the silver/silver halide electrode of the invention is preferably produced by oxidizing the silver metal layer on its surface side with an oxidizing compound containing no heavy metal element in the presence of a halide containing no heavy metal element.
The silver halide layer of the silver/silver halide electrode of the invention is also preferably produced by oxidizing the silver metal layer on its surface side with an oxidizing compound comprising a chelated ferric compound.
The invention further resides in an ion-selective silver/silver halide electrode element comprising, in order, a non-electroconductive support sheet, an electrode composite consisting essentially of a silver metal layer and a silver halide layer, an electrolytic material layer, and an ion-selective layer, the electrode composite being divided to give a pair of electrode units, and further comprising a referential liquid-receiving area and a sample liquid-receiving area each of which is provided on the ion-selective layer above each electrode unit, and a bridge having two terminals, one terminal being placed in the referential liquid-receiving area and another terminal being placed in the sample liquid-receiving area, wherein the silver halide layer contains no heavy metal element.